1. Field of the Invention
The present invention relates to a data processing device for switching between a terminal mode which uses a connection terminal for data communication with an external circuit and an RF (Radio Frequency) mode which uses a radio antenna for data communication with an external circuit.
2. Description of the Related Art
IC cards are available as one type of data processing devices. An IC card comprises a microcomputer in the form of an integrated circuit that is embedded in a plastic card. There have been developed three types of IC cards, i.e., contact cards, contactless cards, and combined cards, that are selectively used depending on the form of signal.
The contact IC cards have a plurality of exposed connection terminals. When a contact IC card is inserted into a card reader, the connection terminals of the contact IC card are brought into individual contact with connection terminals of the card reader. The card reader supplies drive electric power and various signals to the contact IC card, and the microcomputer as a data processing circuit performs various data processings.
The contactless IC cards have one radio antenna for receiving a radio wave transmitted from the card reader. The radio wave from the card reader carries drive electric power and various signals. The IC card extracts the drive electric power and the various signals from the radio wave that is supplied from the card reader via the radio antenna.
The combined IC cards have both a plurality of exposed connection terminals and one radio antenna. A combined IC card is selectively operable in two switchable modes, i.e., a terminal mode in which it operates in the same manner as the contact IC card and an RF mode in which it operates in the same manner as the contactless IC card.
The contact IC card provides better security than the contactless IC card because signals are exchanged between itself and the card reader through a wired connection. The contactless IC card can be handled more easily than the contact IC card since the contactless IC card is not required to be inserted into the card reader.
The combined IC card can be handled easily and provides high security as it can transmit data requiring less security via a contactless connection. As described above, the combined IC card needs to be switched between the terminal mode and the RF mode.
For example, Japanese Patent Laid-Open Publication No. 209592/1991 discloses that the voltage level of drive electric power applied to one of the connection terminals and the voltage level of drive electric power extracted from a received radio wave supplied from the radio antenna are compared with each other, and either of the terminal mode and the RF mode is selected based on the result of the comparison.
Since the voltage levels are generally compared with each other by an analog circuit such as a comparator for mode switching, the mode switching process is performed under analog control. The mode switching process under analog control is problematic in that it is not a clear-cut process and tends to vary due to errors in the fabrication of the combined IC card.
In actual usage of the combined IC card, when unexpected electromagnetic noise is received by the radio antenna, the mode of operation of the combined IC card may possibly switch to the RF mode automatically. If the user, not knowing that the combined IC card is in the RF mode, inserts the combined IC card into a terminal-mode or wired card reader, then the combined IC card may possibly malfunction.
Alternatively, even if the combined IC card inserted in a wired card reader normally operates in the terminal mode, the mode of operation of the combined IC card may switch to the RF mode due to extraneous electromagnetic noise, causing the combined IC card to suffer malfunctioning.
In order to prevent such malfunctioning, the combined IC cards are designed not to operate with radio input signals that do not meet IC card standards. However, because a portable wired card reader is available in the art, a combined IC card thus designed may still be caused to malfunction when the user inserts the combined IC card into such a portable wired card reader that is carried by the user, without recognizing the presence of an RF-mode card reader that is installed nearby.
As described above, when a signal is applied to the radio antenna of a combined IC card and a signal is also applied to the connection terminals thereof at the same time, those simultaneously applied signals may cause the IC card to malfunction and fail. The manufacturer of the combined IC card cannot identify the cause of such malfunctioning and failure because the manufacturer finds it difficult to confirm the environment in which the user uses the combined IC card.